<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8" />
  <meta http-equiv="X-UA-Compatible" content="IE=edge" />
  <meta name="viewport" content="width=device-width, initial-scale=1.0" />
  <title>Document</title>
</head>

<body>
  <a href="https://www.baidu.com">百度</a>

  <form action="">
    <button>登录</button>
  </form>

  <script>
    var link = document.querySelector('a');

    link.addEventListener('click', function (e) {
      e.preventDefault();
      console.log('点击了a元素');
    });

    var form = document.querySelector('form')

    form.addEventListener('submit', function (e) {
      e.preventDefault()
      console.log('点击了from,阻止默认行为');
    })
  </script>
</body>

</html>